The present invention generally relates to device structures and fabrication methods for spintronic devices compatible to back-end integration with semiconductor devices, and more specifically, to spin-based storage elements configured and arranged to provide a stochastically represented multiple state memory function.
Tunnel magnetoresistance (TMR) is a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ) storage element consisting of two ferromagnets separated by a thin insulator. If the insulating layer is thin enough, for example, a few nanometers, electrons can tunnel from one ferromagnet into the other. The digital state in an MTJ is represented by its tunnel resistance. When the two ferromagnet's moments align in parallel with each other, the resistance registers its minimum value, and when they align in antiparallel, its maximum.
Magnetoresistive random access memory (MRAM) is a non-volatile memory that combines a magnetic device with standard silicon-based microelectronics to achieve the combined attributes of non-volatility, high-speed read/write operations, high read/write endurance and data retention. Data is stored in MRAM as magnetic states or characteristics (e.g., magnetization direction, texture of magnetization direction over the area of the MTJ, etc.) instead of electric charges. In one configuration, each MRAM cell includes a transistor, an MTJ device for data storage, a bit line, and a word line. As described above, the MTJ's electrical resistance will be high or low based on the relative magnetic states of certain MTJ layers.